The Dynamo will be back in the MLS postseason after winning on the final day of the season, while United clinched an MLS record it would have preferred not to set.
Houston got on the board first just 10 minutes in. James Riley allowed Giles Barnes to get behind him in the box and the defender was forced to drag the forward down from behind, resulting in a penalty kick. Boniek Garcia stepped up and buried the penalty to give his side an early lead.
United struck back though, as an overlapping Chris Pontius lofted a great cross to the back post from the left flank, and Kyle Porter was on hand to head home from close range to tie the score.
The visitors would regain the lead just five minutes before halftime, and it was a simple sequence from a Brad Davis corner. Barnes cut to the near post and wasn't picked up, allowing him to nod home and restore the lead.
With the result, Houston will have a chance to return to MLS Cup for a third straight season, while United clinched the all-time MLS record for fewest wins in a season with three.